Field of the Invention
The present invention relates to a technique for controlling light irradiation direction by a vehicular lamp (for example, a pair of lamp units) corresponding to an attitude change of a vehicle.
Description of the Background Art
Automatic leveling control for adjusting irradiation direction of light (or the optical axis) of headlamps corresponding to the attitude change of a vehicle in the pitch direction due to occupants or load is known. According to such automatic leveling control, it is possible to prevent glaring an oncoming vehicle or a preceding vehicle even when the attitude of the vehicle changes.
Prior art for achieving automatic leveling control in a moving vehicle is disclosed in Japanese Patent No. 5577080 (hereinafter referred to as Patent Document 1), for example. In the technique disclosed in Patent Document 1, angle of inclination is obtained by performing a predetermined calculation using acceleration values in the horizontal direction and the vertical direction of the vehicle obtained by a two-axis acceleration sensor installed in the vehicle, and the irradiation direction of the light is controlled based on the angle of inclination.
Further, in the technique disclosed in Japanese Patent No. 5787649 (hereinafter referred to as Patent Document 2), acceleration values in the horizontal direction of a vehicle obtained by an acceleration sensor installed in a vehicle is represented on the first axis, and acceleration values in the vertical direction is represented on the second axis, and plots the detected acceleration values in each direction thereby obtaining a straight line from the detection values, and controls the irradiation direction of light based on the slope of the straight line.
However, since the acceleration values outputted from the acceleration sensor in the moving vehicle have a relatively large variation, the calculated attitude angle in the pitch direction of the vehicle based on these acceleration values is also susceptible to variations resulting in a low accuracy of the obtained attitude angle.
In a specific aspect, it is an object of the present invention to provide a technique capable of obtaining the attitude of the vehicle in the pitch direction more accurately.